Antibodies are immunological proteins that bind a specific antigen. In most mammals, including humans and mice, antibodies are constructed from paired heavy and light polypeptide chains. Each chain is made up of two distinct regions, referred to as the variable (Fv) and constant (Fc) regions. The light and heavy chain Fv regions contain the antigen binding determinants of the molecule and are responsible for binding the target antigen. The Fc regions define the class (or isotype) of antibody (IgG for example) and are responsible for binding a number of natural proteins to elicit important biochemical events. The constant region of the heavy chain may be further divided into four smaller domains called: CH1, hinge, CH2 and CH3. A portion of the constant region, the Fc region, is involved in a number of important cellular functions. Generally the Fc region is defined as only comprising CH2 and CH3 and may encompass a portion of the hinge. Given the critical role that the hinge region plays in these cellular functions it will be clear that as used herein, “Fc region” includes the hinge region or portions thereof.
The Fc region of an antibody interacts with a number of Fc receptors and other Fc ligands, imparting an array of important functional capabilities referred to as effector functions. An important family of Fc receptors for the IgG class are the Fc gamma receptors (FcγRs). These receptors mediate communication between antibodies and the cellular arm of the immune system (Raghavan et al., 1996, Annu Rev Cell Dev Biol 12:181-220; Ravetch et al., 2001, Annu Rev Immunol 19:275-290). In humans this protein family includes FcγRI (CID64), including isoforms FcγRIA, FcγRIB, and FcγRIC; FcγRII (CD32), including isoforms FcγRIIA, FcγRIIB, and FcγRIIC; and FcγRIII (CID16), including isoforms FcγRIIIA and FcγRIIIB (Jefferis et al., 2002, Immunol Lett 82:57-65). These receptors typically have an extracellular domain that mediates binding to Fc, a membrane spanning region, and an intracellular domain that may mediate some signaling event within the cell. These different FcγR subtypes are expressed on different cell types (reviewed in Ravetch et al., 1991, Annu Rev Immunol 9:457-492). For example, in humans, FcγRIIIB is found only on neutrophils, whereas FcγRIIIA is found on macrophages, monocytes, natural killer (NK) cells, and a subpopulation of T-cells.
Formation of the Fc/FcγR complex recruits effector cells to sites of bound antigen, typically resulting in signaling events within the cells and important subsequent immune responses such as release of inflammation mediators, B cell activation, endocytosis, phagocytosis, and cytotoxic attack. The ability to mediate cytotoxic and phagocytic effector functions is a potential mechanism by which antibodies destroy targeted cells. The cell-mediated reaction wherein nonspecific cytotoxic cells that express FcγRs recognize bound antibody on a target cell and subsequently cause lysis of the target cell is referred to as antibody dependent cell-mediated cytotoxicity (ADCC) (Raghavan et al., 1996, Annu Rev Cell Dev Biol 12:181-220; Ghetie et al., 2000, Annu Rev Immunol 18:739-766; Ravetch et al., 2001, Annu Rev Immunol 19:275-290). Notably, the primary cells for mediating ADCC, NK cells, express only FcγRIIIA only, whereas monocytes express FcγRI, FcγRII and FcγRIII (Ravetch et al., 1991, supra). Table 1 summarizes several features of the Fc Receptors.
TABLE 1Fc Receptor CharacteristicsFcγRIFcγRII-AFcγRII-B2FcγRII-B1FcγRIIIFcαRIReceptor(CD64)(CD32)(CD32)(CD32)(CD16)FcεRI(CD89)BindingIgG1IgG1IgG1IgG1IgG1IgEIgA1, IgA2108 M−12 × 106 M−12 × 106 M−12 × 106 M−15 × 105 M−11010 M−1107 M−1Cell TypeMacrophageMacrophageMacrophageB cellNK cellMast cellMacrophageNeutrophilNeutrophilNeutrophilsMast cellEosinophilEosinophilNeutrophilEosinophilEosinophilEosinophilsMacrophageBasophilEosinophilDendriticDendriticNeutrophilcellcellMast cellPlateletLangerhancellEffect ofUptakeUptakeUptakeNo uptakeInduction ofSecretion ofUptakeLigationStimulationGranuleInhibition ofInhibition ofKillinggranulesInduction ofActivation ofreleaseStimulationStimulationkillingrespiratoryburstInduction ofkilling
Another important Fc ligand is the complement protein C1q. Fc binding to C1q mediates a process called complement dependent cytotoxicity (CDC) (reviewed in Ward et al., 1995, Ther Immunol 2:77-94). C1q is capable of binding six antibodies, although binding to two IgGs is sufficient to activate the complement cascade. C1q forms a complex with the C1r and C1s serine proteases to form the C1 complex of the complement pathway.
Several key features of antibodies including but not limited to, specificity for target, ability to mediate immune effector mechanisms, and long half-life in serum, make antibodies and related immunoglobulin molecules powerful therapeutics. Numerous monoclonal antibodies are currently in development or are being used therapeutically for the treatment of a variety of conditions including cancer. For example Vitaxin® (MedImmune), a humanized Integrin αvβ3 antibody (e.g., PCT publication WO 2003/075957), Herceptin® (Genentech), a humanized anti-Her2/neu antibody approved to treat breast cancer (e.g., U.S. Pat. No. 5,677,171), CNTO 95 (Centocor), a human Integrin αv antibody (PCT publication WO 02/12501), Rituxan® (IDEC/Genentech/Roche), a chimeric anti-CD20 antibody approved to treat Non-Hodgkin's lymphoma (e.g., U.S. Pat. No. 5,736,137) and Erbitux® (ImClone), a chimeric anti-EGFR antibody (e.g., U.S. Pat. No. 4,943,533).
There are a number of possible mechanisms by which antibodies destroy tumor cells, including anti-proliferation via blockage of needed growth pathways, intracellular signaling leading to apoptosis, enhanced down regulation and/or turnover of receptors, ADCC, CDC, and promotion of an adaptive immune response (Cragg et al., 1999, Curr Opin Immunol 11:541-547; Glennie et al., 2000, Immunol Today 21:403-410). However, despite widespread use, antibodies are not optimized for clinic use and many have suboptimal anticancer potency. Thus, there is a significant need to enhance the capacity of antibodies to destroy targeted cancer cells. Methods for enhancing the anti-tumor-potency of antibodies via enhancement of their ability to mediate cytotoxic effector functions such as ADCC and CDC are particularly promising. The importance of FcγR-mediated effector functions for the anti-cancer activity of antibodies has been demonstrated in mice (Clynes et al., 1998, Proc Natl Acad Sci USA 95:652-656; Clynes et al., 2000, Nat Med 6:443-446), and the affinity of the interaction between Fc and certain FcγRs correlates with targeted cytotoxicity in cell-based assays (Shields et al., 2001, J Biol Chem 276:6591-6604; Presta et al., 2002, Biochem Soc Trans 30:487-490; Shields et al., 2002, J Biol Chem 277:26733-26740). Together these data suggest that manipulating the binding ability of the Fc region of an IgG1 antibody to certain FcγRs may enhance effector functions resulting in more effective destruction of cancer cells in patients. Furthermore, because FcγRs can mediate antigen uptake and processing by antigen presenting cells, enhanced Fc/FcγR affinity may also improve the capacity of antibody therapeutics to elicit an adaptive immune response.
While enhancing effector function can increase the capacity of antibodies to destroy target cells, for some antibody therapies reduced or eliminated effector function may be more desirable. This is particularly true for those antibodies designed to deliver a drug (e.g., toxins and isotopes) to the target cell where the Fc/FcγR mediated effector functions bring healthy immune cells into the proximity of the deadly payload, resulting in depletion of normal lymphoid tissue along with the target cells (Hutchins et al., 1995, PNAS USA 92:11980-11984; White et al., 2001, Annu Rev Med 52:125-145). In these cases the use of Fc variants that poorly recruit complement or effector cells would be of tremendous benefit (see for example, Wu et al., 2000, Cell Immunol 100:16-26; Shields et al., 2001, J. Biol Chem 276:6591-6604; U.S. Pat. No. 6,194,551; U.S. Pat. No. 5,885,573 and PCT publication WO 04/029207).
All FcγRs bind the Fc region of the IgG subclass, but with different affinities (e.g., FcγRI is a high affinity while FcγRII and FcγRIII are low affinity binders. Other differences between the FcγRs are mechanistic. For example, FcγRI, FcγRIIA/C, and FcγRIIIA are positive regulators of immune complex triggered activation, characterized by having an immunoreceptor tyrosine-based activation motif (ITAM) while FcγRIIB has an immunoreceptor tyrosine-based inhibition motif (ITIM) and is therefore inhibitory. Thus, the balance between activating and inhibiting receptors is an important consideration. For example, enhancing Fc binding to the positive regulators (e.g., FcγRIIIA) while leaving unchanged or even reducing Fc binding to the negative regulator FcγRIIB could result in optimized effector function such as enhanced ADCC mediated destruction of tumor cells. Another critical consideration is that Fc variants should be engineered such that the binding to FcγRs and/or C1q is modulated in the desired manner but so that they maintain their stability, solubility, structural integrity as well as their ability to interact with other important Fc ligands such as FcRn and staphylococcal protein A, streptococcal protein G.
Antibodies of the IgG isotype are exceptionally flexible molecules. The structure primarily responsible for the internal flexibility of IgG molecules is located between the first (CH1) and second (CH2) domains of the constant region, and is termed the hinge. The hinge can be divided into three peptide regions; upper, middle and lower hinge respectively Brekke et al., 1995, Immunol Today 16: 85-90. Several studies indicate that the hinge region is essential for activation of the complement cascade by IgGs (Klein et al., 1981 Proc Natl Acad Sci USA 78: 524-8; Mechaelsen et al., 1990, Scand J Immunol. 32: 517-28). In other studies one group has demonstrated that the lower hinge region is also involved in contact with FcγRs (Radaev and Sun, 2001, Immunology 38:1073-1083). Likewise, the nature of the hinge region also influences binding to FcγRs as well as ADCC activity (Redpath et al., 1998, Human Immunology; 59: 720-7; Gillies and Wesolowsi, 1990, Hum. Antibod. Hybridomas 1: 47-54).
Numerous mutagenesis studies have been carried out on the hinge domain however there is little consensus as to how alterations of the hinge region affect function. For example, some studies indicate that, generally speaking, reducing the hinge flexibility or length results in a decrease in complement fixation/activation (Oi et al., 1984, Nature 307:136-40; Dangl et al., 1988, EMBO 71989-94). Conversely, other studies suggest that a reduction in hinge flexibility or length directly correlates with an increase in complement activation (Brekke et al., 1993, Nature 363:628-30; Bastida-Corcuera et al., 1999, Vet Immunol Immunopathol 71:115-123; Redpath et al., 1998, Human Immunol. 59:720-7; Sandlie et al., 1989, Eur J Immunol 19:1599-603; Michaelsen et al., 1994, U.S. Pat. No. 5,348,876; Norderhaug et al. 1991, Eur J Immunol 21:2379-3284) whereas a third set of studies indicates the lack of such a simple correlation (Shopes et al., 1993, Mol. Immunol. 30:603-9; Brekke et al., 1993, Nature 363:628-30; Brekke et al., 1995, Immunol. Today 16:85-90; Tan et al., 1990, PNAS USA 87:162-166; Tan et al., 1991, PNAS USA 88:5066; Coloma et al., 1997, J. Immunol. 158:733-40). One set of studies suggest that the “openness” status of the hinge region may play a role (Schauenstein et al., 1986, Int Arch Allergy Appl Immunol 80:174-9; Schauenstein et al., 1996, Biochem Mol Biol Int 40:433-446; Stevenson et al., 1997, J Immunol 158:2242-50). Although many of the previous studies appear to give contradictory interpretations of the relationship between the structure and function of the hinge, it is important to recognize that many of the previous studies were performed using disparate techniques and in many cases on molecules of different IgG subtypes. Thus, interpretation and extrapolation of previous studies is difficult. Given the importance of the hinge region in mediating antibody function the ability to specifically modify the hinge in order to modulate Fc function would be a useful tool in developing therapeutics for the treatment and prevention of numerous diseases and disorders. The present invention provides a detailed analysis of the hinge region and the identification of specific classes of modifications useful for the modulation of Fc ligand binding and effector function.
2.1 Diseases of Relevance
Several key features of antibodies including but not limited to, specificity for target, ability to mediate immune effector mechanisms, and long half-life in serum, make antibodies powerful therapeutics. Numerous monoclonal antibodies are currently in development or are being used therapeutically for the treatment of a variety of conditions including cancer. The ability to modulate the effector binding and function of any particular antibody would be of tremendous benefit in adapting an antibody for the treatment of a disease or disorder. Diseases for which antibody therapeutics are particularly well suited are described below.
2.1.1 Cancer
A neoplasm, or tumor, is a neoplastic mass resulting from abnormal uncontrolled cell growth, which can be benign or malignant. Benign tumors generally remain localized. Malignant tumors are collectively termed cancers. The term “malignant” generally means that the tumor can invade and destroy neighboring body structures and spread to distant sites to cause death (for review, see Robbins and Angell, 1976, Basic Pathologic 2d Ed., W.B. Saunders Co., Philadelphia, pp. 68-122). Cancer can arise in many sites of the body and behave differently depending upon its origin. Cancerous cells destroy the part of the body in which they originate and then spread to other part(s) of the body where they start new growth and cause more destruction.
More than 1.2 million Americans develop cancer each year. Cancer is the second leading case of death in the United States and if current trends continue, cancer is expected to be the leading cause of the death by the year 2010. Lung and prostate cancer are the top cancer killers for men in the United States. Lung and breast cancer are the top cancer killers for women in the United States. One in two men in the United States will be diagnosed with cancer at some time during his lifetime. One in three women in the United States will be diagnosed with cancer at some time during her lifetime.
Currently, cancer therapy may involve surgery, chemotherapy, hormonal therapy and/or radiation treatment to eradicate neoplastic cells in a patient (See, for example, Stockdale, 1998, “Principles of Cancer Patient Management”, in Scientific American: Medicine, vol. 3, Rubenstein and Federman, eds., Chapter 12, Section IV). Recently, cancer therapy could also involve biological therapy or immunotherapy. All of these approaches pose significant drawbacks for the patient. Surgery, for example, may be contraindicated due to the health of the patient or may be unacceptable to the patient. Additionally, surgery may not completely remove the neoplastic tissue. Radiation therapy is only effective when the neoplastic tissue exhibits a higher sensitivity to radiation than normal tissue, and radiation therapy can also often elicit serious side effects. Hormonal therapy is rarely given as a single agent and although can be effective, is often used to prevent or delay recurrence of cancer after other treatments have removed the majority of the cancer cells. Biological therapies/immunotherapies are limited in number and may produce side effects such as rashes or swellings, flu-like symptoms, including fever, chills and fatigue, digestive tract problems or allergic reactions.
With respect to chemotherapy, there are a variety of chemotherapeutic agents available for treatment of cancer. A significant majority of cancer chemotherapeutics act by inhibiting DNA synthesis, either directly, or indirectly by inhibiting the biosynthesis of the deoxyribonucleotide triphosphate precursors, to prevent DNA replication and concomitant cell division (See, for example, Gilman et al., Goodman and Gilman's: The Pharmacological Basis of Therapeutics, Eighth Ed. (Pergamom Press, New York, 1990)). These agents, which include alkylating agents, such as nitrosourea, anti-metabolites, such as methotrexate and hydroxyurea, and other agents, such as etoposides, campathecins, bleomycin, doxorubicin, daunorubicin, etc., although not necessarily cell cycle specific, kill cells during S phase because of their effect on DNA replication. Other agents, specifically colchicine and the vinca alkaloids, such as vinblastine and vincristine, interfere with microtubule assembly resulting in mitotic arrest. Chemotherapy protocols generally involve administration of a combination of chemotherapeutic agents to increase the efficacy of treatment.
Despite the availability of a variety of chemotherapeutic agents, chemotherapy has many drawbacks (See, for example, Stockdale, 1998, “Principles Of Cancer Patient Management” in Scientific American Medicine, vol. 3, Rubenstein and Federman, eds., ch. 12, sect. 10). Almost all chemotherapeutic agents are toxic, and chemotherapy causes significant, and often dangerous, side effects, including severe nausea, bone marrow depression, immunosuppression, etc. Additionally, even with administration of combinations of chemotherapeutic agents, many tumor cells are resistant or develop resistance to the chemotherapeutic agents. In fact, those cells resistant to the particular chemotherapeutic agents used in the treatment protocol often prove to be resistant to other drugs, even those agents that act by mechanisms different from the mechanisms of action of the drugs used in the specific treatment; this phenomenon is termed pleiotropic drug or multidrug resistance. Thus, because of drug resistance, many cancers prove refractory to standard chemotherapeutic treatment protocols.
There is a significant need for alternative cancer treatments, particularly for treatment of cancer that has proved refractory to standard cancer treatments, such as surgery, radiation therapy, chemotherapy, and hormonal therapy. A promising alternative is immunotherapy, in which cancer cells are specifically targeted by cancer antigen-specific antibodies. Major efforts have been directed at harnessing the specificity of the immune response, for example, hybridoma technology has enabled the development of tumor selective monoclonal antibodies (See Green M. C. et al., 2000 Cancer Treat Rev., 26: 269-286; Weiner L M, 1999 Semin Oncol. 26(suppl. 14): 43-51), and in the past few years, the Food and Drug Administration has approved the first MAbs for cancer therapy: Rituxin (anti-CD20) for non-Hodgkin's Lymphoma and Herceptin [anti-(c-erb-2/HER-2)] for metastatic breast cancer (Suzanne A. Eccles, 2001, Breast Cancer Res., 3: S6-90). However, the potency of antibody effector function, e.g., to mediate antibody dependent cellular cytotoxicity (“ADCC”) is an obstacle to such treatment. Methods to improve the efficacy of such immunotherapy are thus needed.
2.1.2 Inflammatory Diseases and Autoimmune Diseases
Inflammation is a process by which the body's white blood cells and chemicals protect our bodies from infection by foreign substances, such as bacteria and viruses. It is usually characterized by pain, swelling, warmth and redness of the affected area. Chemicals known as cytokines and prostaglandins control this process, and are released in an ordered and self-limiting cascade into the blood or affected tissues. This release of chemicals increases the blood flow to the area of injury or infection, and may result in the redness and warmth. Some of the chemicals cause a leak of fluid into the tissues, resulting in swelling. This protective process may stimulate nerves and cause pain. These changes, when occurring for a limited period in the relevant area, work to the benefit of the body.
In autoimmune and/or inflammatory disorders, the immune system triggers an inflammatory response when there are no foreign substances to fight and the body's normally protective immune system causes damage to its own tissues by mistakenly attacking self. There are many different autoimmune disorders that affect the body in different ways. For example, the brain is affected in individuals with multiple sclerosis, the gut is affected in individuals with Crohn's disease, and the synovium, bone and cartilage of various joints are affected in individuals with rheumatoid arthritis. As autoimmune disorders progress destruction of one or more types of body tissues, abnormal growth of an organ, or changes in organ function may result. The autoimmune disorder may affect only one organ or tissue type or may affect multiple organs and tissues. Organs and tissues commonly affected by autoimmune disorders include red blood cells, blood vessels, connective tissues, endocrine glands (e.g., the thyroid or pancreas), muscles, joints, and skin. Examples of autoimmune disorders include, but are not limited to, Hashimoto's thyroiditis, pernicious anemia, Addison's disease, type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, dermatomyositis, Sjogren's syndrome, dermatomyositis, lupus erythematosus, multiple sclerosis, autoimmune inner ear disease myasthenia gravis, Reiter's syndrome, Graves disease, autoimmune hepatitis, familial adenomatous polyposis and ulcerative colitis.
Rheumatoid arthritis (RA) and juvenile rheumatoid arthritis are types of inflammatory arthritis. Arthritis is a general term that describes inflammation in joints. Some, but not all, types of arthritis are the result of misdirected inflammation. Besides rheumatoid arthritis, other types of arthritis associated with inflammation include the following: psoriatic arthritis, Reiter's syndrome, ankylosing spondylitis arthritis, and gouty arthritis. Rheumatoid arthritis is a type of chronic arthritis that occurs in joints on both sides of the body (such as both hands, wrists or knees). This symmetry helps distinguish rheumatoid arthritis from other types of arthritis. In addition to affecting the joints, rheumatoid arthritis may occasionally affect the skin, eyes, lungs, heart, blood or nerves.
Rheumatoid arthritis affects about 1% of the world's population and is potentially disabling. There are approximately 2.9 million incidences of rheumatoid arthritis in the United States. Two to three times more women are affected than men. The typical age that rheumatoid arthritis occurs is between 25 and 50. Juvenile rheumatoid arthritis affects 71,000 young Americans (aged eighteen and under), affecting six times as many girls as boys.
Rheumatoid arthritis is an autoimmune disorder where the body's immune system improperly identifies the synovial membranes that secrete the lubricating fluid in the joints as foreign. Inflammation results, and the cartilage and tissues in and around the joints are damaged or destroyed. In severe cases, this inflammation extends to other joint tissues and surrounding cartilage, where it may erode or destroy bone and cartilage and lead to joint deformities. The body replaces damaged tissue with scar tissue, causing the normal spaces within the joints to become narrow and the bones to fuse together. Rheumatoid arthritis creates stiffness, swelling, fatigue, anemia, weight loss, fever, and often, crippling pain. Some common symptoms of rheumatoid arthritis include joint stiffness upon awakening that lasts an hour or longer; swelling in a specific finger or wrist joints; swelling in the soft tissue around the joints; and swelling on both sides of the joint. Swelling can occur with or without pain, and can worsen progressively or remain the same for years before progressing.
The diagnosis of rheumatoid arthritis is based on a combination of factors, including: the specific location and symmetry of painful joints, the presence of joint stiffness in the morning, the presence of bumps and nodules under the skin (rheumatoid nodules), results of X-ray tests that suggest rheumatoid arthritis, and/or positive results of a blood test called the rheumatoid factor. Many, but not all, people with rheumatoid arthritis have the rheumatoid-factor antibody in their blood. The rheumatoid factor may be present in people who do not have rheumatoid arthritis. Other diseases can also cause the rheumatoid factor to be produced in the blood. That is why the diagnosis of rheumatoid arthritis is based on a combination of several factors and not just the presence of the rheumatoid factor in the blood.
The typical course of the disease is one of persistent but fluctuating joint symptoms, and after about 10 years, 90% of sufferers will show structural damage to bone and cartilage. A small percentage will have a short illness that clears up completely, and another small percentage will have very severe disease with many joint deformities, and occasionally other manifestations of the disease. The inflammatory process causes erosion or destruction of bone and cartilage in the joints. In rheumatoid arthritis, there is an autoimmune cycle of persistent antigen presentation, T-cell stimulation, cytokine secretion, synovial cell activation, and joint destruction. The disease has a major impact on both the individual and society, causing significant pain, impaired function and disability, as well as costing millions of dollars in healthcare expenses and lost wages. (See, for example, the NIH website and the NIAID website).
Currently available therapy for arthritis focuses on reducing inflammation of the joints with anti-inflammatory or immunosuppressive medications. The first line of treatment of any arthritis is usually anti-inflammatories, such as aspirin, ibuprofen and Cox-2 inhibitors such as celecoxib and rofecoxib. “Second line drugs” include gold, methotrexate and steroids. Although these are well-established treatments for arthritis, very few patients remit on these lines of treatment alone. Recent advances in the understanding of the pathogenesis of rheumatoid arthritis have led to the use of methotrexate in combination with antibodies to cytokines or recombinant soluble receptors. For example, recombinant soluble receptors for tumor necrosis factor (TNF)-α have been used in combination with methotrexate in the treatment of arthritis. However, only about 50% of the patients treated with a combination of methotrexate and anti-TNF-α agents such as recombinant soluble receptors for TNF-α show clinically significant improvement. Many patients remain refractory despite treatment. Difficult treatment issues still remain for patients with rheumatoid arthritis. Many current treatments have a high incidence of side effects or cannot completely prevent disease progression. So far, no treatment is ideal, and there is no cure. Novel therapeutics are needed that more effectively treat rheumatoid arthritis and other autoimmune disorders.
2.1.3 Infectious Diseases
Infectious agents that cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms). The remarkable variety of these pathogens has caused the natural selection of two crucial features of adaptive immunity. First, the advantage of being able to recognize a wide range of different pathogens has driven the development of receptors on B and T cells of equal or greater diversity. Second, the distinct habitats and life cycles of pathogens have to be countered by a range of distinct effector mechanisms. The characteristic features of each pathogen are its mode of transmission, its mechanism of replication, its pathogenesis or the means by which it causes disease, and the response it elicits.
The record of human suffering and death caused by smallpox, cholera, typhus, dysentery, malaria, etc. establishes the eminence of the infectious diseases. Despite the outstanding successes in control afforded by improved sanitation, immunization, and antimicrobial therapy, the infectious diseases continue to be a common and significant problem of modern medicine. The most common disease of mankind, the common cold, is an infectious disease, as is the feared modern disease AIDS. Some chronic neurological diseases that were thought formerly to be degenerative diseases have proven to be infectious. There is little doubt that the future will continue to reveal the infectious diseases as major medical problems.
An enormous number of human and animal diseases result from virulent and opportunistic infections from any of the above mentioned infectious agents (see Belshe (Ed.) 1984 Textbook of Human Virology, PSG Publishing, Littleton, Mass.).
One category of infectious diseases are viral infections for example. Viral diseases of a wide array of tissues, including the respiratory tract, CNS, skin, genitourinary tract, eyes, ears, immune system, gastrointestinal tract, and musculoskeletal system, affect a vast number of humans of all ages (see Table 328-2 In: Wyngaarden and Smith, 1988, Cecil Textbook of Medicine, 18th Ed., W.B. Saunders Co., Philadelphia, pp. 1750-1753). Although considerable effort has been invested in the design of effective anti-viral therapies, viral infections continue to threaten the lives of millions of people worldwide. In general, attempts to develop anti-viral drugs have focused on several stages of viral life cycle (See e.g., Mitsuya et al., 1991, FASEB J. 5:2369-2381, discussing HIV). However, a common drawback associated with using of many current anti-viral drugs is their deleterious side effects, such as toxicity to the host or resistance by certain viral strains.
Citation or discussion of a reference herein shall not be construed as an admission that such is prior art to the present invention.